Browsing by Author "Tseng, Chih-Han"

Now showing 1 - 3 of 3

Comparison of oxidation in uni-directionally and randomly oriented Cu films for low temperature Cu-to-Cu direct bonding
(2018-07-13)
Tseng, Chih-Han
;
Tu, K. N.
;
Chen, Chih
;
材料科學與工程學系
;
國際半導體學院
Cu-to-Cu direct bonding has attracted attention because it has been implemented in CMOS image sensors. Prior to the bonding, the oxides on the Cu surface needs to be removed, yet the surface may oxidize right after cleaning. Thus, oxidation is an inherent issue in the application of Cu direct bonding. Our previous study reported that Cu direct bonding can be achieved below 250 degrees C by using (111)-oriented nanotwinned Cu because it has the fastest surface diffusivity. However, the oxidation behavior of the nanotwinned Cu is unclear. Here, we examined the oxidation behavior of highly (111) and (200) oriented, and randomly-oriented Cu films at temperatures ranging from 120 to 250 degrees C. Transmission electron microscopy was used to measure the oxide thickness. The results show that the oxidation rate of (111)-oriented nanotwinned Cu has the lowest oxidation rate among them. Together, it is unique to possess the combination of the fastest surface diffusivity and the lowest oxidation rate.
Growth of Highly (111)-Oriented Nanotwinned Cu with the Addition of Sulfuric Acid in CuSO4 Based Electrolyte
(2019-01-01)
Tseng, Chih-Han
;
Chen, Chih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We reported that highly (111)-oriented nanotwinned Cu (nt-Cu) can be grown by DC electroplating using a CuSO4 based electrolyte in our previous study. However, in practical applications, the addition of H2SO4 is required to improve uniformity of the Cu films. In this study, we added H2SO4 in the CuSO4 based electrolyte with different concentrations, ranging from SO to 110 g/L. It is found that nt-Cu can be fabricated with the addition of the H2SO4 acid at the current densities from 5 A/dm(2) to 11 A/dm(2). The ratios of (111) to (200) or (111) to (220) X-ray reflections are extremely high, indicating that the (111) preferred orientation is very strong. The texture fraction and texture coefficient could not precisely determine which Cu films contain columnar (111) nt-Cu grains. We propose a criteria to predict the columnar (111) nt-Cu microstructure by the ratios of (111) to (200) and (111) to (220) X-ray reflections. When both ratios exceed 1000, the fabricated Cu films could possess columnar (111) nt-Cu grains.
Low-temperature and low pressure copper-to-copper direct bonding enabled by creep on highly (111)-oriented Cu surfaces
(2015)
Tseng, Chih-Han
;
Liu, Chien-Min
;
Lin, Han-wen
;
Chu, Yi-Cheng
;
Chen, Chih
Cu-to-Cu microbumps have many advantages, such as better electrical and thermal conductivities. The Cu-to-Cu microbumps may be a potential solution to the heat dissipation problem in 3D IC integration. In addition, for packaging of CMOS image sensors, the bonding temperature is preferred to below 200 degrees C. Therefore, low temperature and low pressure Cu-to-Cu direct is of great interests for packaging industry. However, it is a challenging issue because Cu atoms diffuse slowly below 200 degrees C. In this study, we achieved low temperature and low pressure Cu bonding using highly (111)-orientated Cu films. Because the diffusivity of Cu atoms on the (111) surface diffusivity is the fastest among all the crystallographic planes of Cu. The bonding temperature can be lowered to 150 degrees C at a compressive stress of 114 psi held for 60 min at 10-3 torr. Since the melting points of popular Pb-free solders such as SnAg and SnAgCu are over 230 degrees C. Therefore the present technique can be applied to packaging of CMOS image sensors and 3D IC integration.